The nitrification inhibition (NI) bioassay guided fractionation of the methanol extract of lyophilized and milled roots of Leuceana leucocephala resulted in the isolation of four compounds, 1-4, as confirmed from their 1H and 13C NMR spectral data. Compound 1, gallocatechin, was the most active NI inhibitor at 12 microg/mL. Epigallocatechin, 2, and epicatechin, 4, isolated as mixtures, were not assayed individually for their NI inhibitory activities against the nitrification bacterium Nitrosomonas europaea.